To achieve shaping and cleaning of oysters during grow-out, oyster farmers utilize cages, baskets, bags, trays or other containers that are moved, operated, or handled solely by human interaction with the grow-out container. In addition, to achieve desired shape, tumbling is required to shape the oyster to a deep cup, rather than flat shell, for a bigger meat size per shell ratio. Some grow-out locations have bio-fouling problems that require oysters to be cleaned in tumbler washers or power washed in the containers. Bio-fouling occurs when organisms in the water column attach to the oyster, inhibiting growth and feeding opportunity. For example, this is the case with mud worms that settle on the oysters, creating a blanket of mud or silt over the oysters.
To achieve a survival grow-out to the marketplace, farmers must come into contact with the containers of oysters for tumbling and cleaning on a regular basis. As short an interval as every two weeks, depending on the location, may be necessary. If left alone, the oyster would be misshapen and undesirable for sale or result in mortality from bio-fouling.
The problems that are faced vary from farm to farm, depending on the grow-out location. In areas where bio-fouling is a major problem, farms must hire extra labor just to clean the oysters so that they survive. For inter-tidal grow out locations, pumps and hoses must be dragged around the farm to wash the oysters. Most farmers in sub-tidal (constantly submerged) grow-out locations use cages for the oysters to grow in while on the bottom. They also may be using containers inside of large cages. This requires lifting the containment structure off the bottom in order to clean the oysters in washers.
Tumbling for shape requires dumping each container into a land or vessel based tumbler, which chips some new growth to encourage the oyster to grow a deeper cup. Tumbling for shape in sub-tidal applications requires taking every container off the bottom and dumping them into a vessel based tumbler to chip new growth and wash the oyster. The washing needs to take place if the bio-fouling has proliferated, regardless whether or not the oysters need to be chipped for shaping.
There is a downside to chipping aggressively by tumbling oysters in a land or vessel based tumbler. The rate of speed at which oysters must be tumbled to get through the farm can be problematic. At aggressive tumbling speeds, oysters can be damaged to the point where they have broken the seal around the lip of the shell and must be put back in the water to repair themselves. If damaged too much, the oysters will die.